The costs associated with drug development are enormous. Improving the effectiveness of existing drug therapies has led to the design of new materials for drug delivery. For example, many protein drugs, such as nerve growth factor (NGF), have attracted growing interests for the treatment of neurodegenerative disorders, such as Alzheimer's disease. However, the uses of these drugs are still hampered by a lack of an effective route and method of delivery. This is partly because these protein drugs have very short half-lives, have difficultly crossing biological barriers, and are easily metabolized at other tissue sites. In addition, current available drug delivery systems can not achieve targeted and long-term drug release while at the same time responding to environmental changes (such as temperature, pH, etc.) which are caused by many disorders in organs and blood vessels.
Biodegradable polymers play an important role in drug delivery. Because these polymers degrade after a certain period of time, sustained drug release can be enhanced and surgical removal after drug depletion can be avoided. However, many biodegradable polymers have disadvantages in requiring organic solvents for drug loading thereby limiting the selection of drugs that are not adversely affected, i.e. denaturation of protein drugs, by such solvents. Biodegradable polymers also suffer from inconsistent drug release kinetics and lack of response to physiological changes in living organisms. Bioresponsive polymers are another class of polymers widely studied, especially as devices for the delivery of physiological unstable agents, such as protein drugs including growth factors. This class of materials is responsive to physical, chemical, or biological stimuli. However, bioresponsive polymers have problems in non-biodegradability and non-sustained drug release.
Accordingly, a continuing need exists for the development of new materials that can be tuned to biologically activity and precise drug delivery vehicles and for other related uses.